Apparatus for the manufacture of compliant cable



June 7, 1966 M. P. EHRLICH 3,254,369

APPARATUS FOR THE MANUFACTURE OF COMPLIANT CABLE Original Filed Nov. 3,1961 INVENTOR.

MlLV/N R HRL/CH DTf RNI'YS United States Patent 3,254,369 APPARATUS FORTHE MANUFACTURE OF COMPLIANT CABLE Melvin P. Ehrlich, Plainview, N.Y.,assignor to Nuclear 3 Claims. (Cl. 18-13) The present invention relatesgenerally to compliant electrical cables and like devices, and inparticular to an apparatus for manufacturing longitudinally compliantelectrical cables of the multiple conductor and coaxial types, and toimprovements in the construction of such cables. This is a division ofmy copending application, Serial No. 150,093, entitled Electrical Deviceand Method of Manufacture filed on November 3, 1961, now abandoned.

Many type of electrical cables are available for the transmission ofsignal energy from one point to another, with reasonably low signalattenuation. However, of recent times there has developed a need forelectrical cables which are capable of transmitting signal energy fromone point to another with a high order of mechanical decoupling. Atypical application is in underwater detection systems of the sonobuoytype wherein an underwater hydro-phone is suspended from a float on thesurface of a body of water by a longitudinally compliant cable whichmakes electrical connection from the underwater hydro-phone to atransmitter carried by the float. Signals picked up by the hydro-phoneor the microphone are fed via the electrical cable to the transmitterwhich in turn transmits the detected signals to an appropriate monitor,such as an overhead airplane or the like. A primary requisite for thistype of system is that the drag exerted by the pendent cable andhydro-phone does not cause the float containing the transmitter to bepulled under the surface or upset for this would disrupt signaltransmission to the monitor and at best provide intermittent operation.Further, the use of a longitudinally compliant cable between theunderwater hydro-phone and the surface float and transmitter effectivelyreduces the generation of spurious signals which manifest themselves asundesired noises in the system. Accordingly, there exists a need for anelectrical cable, which apart from its signal transmission properties,serves as a mechanical decoupling when connected in a system where thecable is stretched and loaded. Preferably for use in this environment,the cable should also be relatively inexpensive to manufacture since itwill be expendible along with the remaining'components of the sonobuoysystem.

Broadly, it is an object of the present invention to provide an extruderapparatus for the extrusion of sheathing material about a core.templation of the present invention to provide an extruder head adaptedto receive a core about which is deposited a sheathing material toproduce an assembled core and extruded sheathing.

In accordance with the present invention, there is provided an extruderhead comprising a body which is formed with a central cavity and acircular extrusion orifice in communication with the cavity. The wallsof the cavity, adjacent the extrusion orifice are formed infrustroconical fashion decreasing in diameter toward said orifice. Anextruder pipe is connected to the body of the extruder head, incommunication with the cavity, at a location removed from the extrusionorifice. A torpedo is mounted within the cavity and in alignment withthe extrusion orifice and includes a central opening along its axis forthe passage of a core into the extruder head, through Specifically, itis within the con-- the torpedo and out of the extruder head through theextrusion orifice. The torpedo is formed at its end'adjacent the orificewith frustro-conical walls of decreasing diameter toward the orifice.The included angle of the frust-conical torpedo walls is less than theincluded angle of the frustro-conical cavity walls thereby defining anannular outlet passage from the cavity of decreasing crosssection towardthe extrusion orifice between the cavity walls and the walls of thetorpedo.

The above brief description, as well as further objects, features andadvantages of the present invention will 'be more fully appreciated byreference to the following detailed description of an illustrativeembodiment of the present invention, when taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is an elevational view of a length of a core of resilientelastomeric material which is longitudinally distensible, shown in arelaxed condition preliminary to the formation thereon of a first orinner electrical conductor;

FIG. 2 is an elevational view showing the core of FIG.

1 distended to approximately twice its length and having supportedthereon a first or inner conductor in the form of a braid includingintertwined electrically conducting and reinforcing strands;

FIG. 3 is an elevational view, with parts in section, showing anextrusion system for forming an insulating sheath about the core andconductor sub-assembly shown in FIG. 2 and further showing a means forcuring the in sulating sheath; and,

FIG. 4 is an elevational. View of a partially completed length ofcomplant cable formed with an extruded insulating sheath by theextrusion and curing apparatus shown in FIG. 3.

Referring now specifically to the drawings, reference will be made to atypical extensible cable assembly and the process of its manufacture inorder to show the usefulness and function of the apparatus according tothe present invention.

Referring first to FIG. 1, there is shown a typical inner core 20 ofresilient elastomeric material which is 1ongi tudinally distensible andserves as a supporting mandrel during the successive cable-forming stepsand ultimately as the inner stretchable support for the final cable.Various types of elastomeric materials are suitable for the manufactureof the core. In a typical commercial embodiment, the core may befabricated of an extruded silicone elastomer. A typical siliconeelastomer is manufactured by the Silicone Division of Union CarbideCorporation under the trademark Union Carbide KW 1300. The durometer andcross section of the elastomeric core 20 is selected to enable therequired longitudinal distension thereof without exceeding the tensilestrength of the material. In a typical coaxial cable, the core 20 iscircular in cross section and has an outer diameter of the order ofmils.

Referring to FIG. 2, there is shown the elastomeric core 20 stretched toin excess of twice its length and having supported thereon a conductor22 of electrically conducting material arranged in a configuration to belongitudinally distensible. In this illustrative embodiment, theconductor 22 is a braiding of electrically conducting strands 22a andreinforcing strands 22b. In a typical construction, the electricallyconducting strands 22a may be of copper, While the reinforcing strands22b may be of an appropriate synthetic having relatively good tensilestrength, such as nylon or Dacron. The inner braided conductor 22 isformed on a conventional braiding machine with provision forprestretching the core 20 to establish the desired degree of compliance.In braiding 3 the inner conductor 22, the number of braids per inch isestablished such that the interstices between successive braids allowthe core 2t) with the braided inner conductor 22 thereon to return toapproximately the same length as the core 26 without the braided innerconductor 22 (see P16. 1).

The sub-assembly of the elastomeric core 20 and thelongitudinally-distensible inner conductor 22 is preferably providedwith an extruded intermediate insulating sheath 24 of an elastomericmaterial by the improved extrusion apparatus according to the presentinvention, shown in FIG. 3 and generally designated by the referencenumeral 26. The extrusion apparatus 26 includes a substantiallyhorizontally extending extruder outlet pipe 28 which feeds theelastomeric material from a conventional extruder to an extruder die orhead 39 provided with a cavity 32 terminating at its lower end in anextrusion orifice or Venturi. aperture 34. Extending longitudinally ofthe cavity 32 towards the aperture or orifice 34 is the torpedo 36 ofthe extrusion die or head 39 which is mounted in any appropriate fashionand provides an axial through passage for feeding the sub-assembly ofthe core 20 and the inner conductor 22 through the extrusion die or head39. The frustro-conical tip 36a of the torpedo 36 and the coextensivefrustro-conical bounding wall 3%. of the die 30 are arranged relative toeach other to provide an annular outlet passage 32a of progressivelydecreasing cross section which communicates with the Venturi aperture34. The decreasing cross section of the annular outlet passage 32 bringsabout an increase in the pressure and velocity of the extruded materialas it flows towards the Venturi aperture 34 which establishes a rate offlow at the interface between the extruded material of the insulatingsheath and the sub-assembly 20, 22 to provide a linear feed of thesub-assembly at a rate that will establish an insulating sheath 24 of adesired cross section without elongating or pulling on the sub-assembly20, 22. After the extruded sheath 24 and the encased sub-assembly 26, 22leave the extrusion aperture 34, the rate of feed is materiallydecreased due to the so-called Venturi action. However, during thecrucial period when the extruded material flows into contact with thesubassembly, 20, 22, the increased pressure and velocity is sufiicientto achieve the desired rate of linear feed of the sub-assembly 20, 22and the insulating sheath 24 is extruded onto the sub-assembly while thelatter is substantially tensionless and in a relaxed condition. The axisof the extruding die or head 34} and of the torpedo 36 is disposed at anobtuse angle with respect to the axis of the extruder outlet pipe 28such that the component of extruder pressure available axially in theextruder head 30 (which will act in the direction of linear advance ofthe sub-assembly 2t), 22) is somewhat greater than in an arrangementwherein the axis of the extruder head 30 would be disposed atapproximately a right angle to the axis of the extruder outlet pipe 28.The torpedo 36 is mounted within the extruder head 30 at the endopposite from the orifice 34 by means of a threaded shaft extension 3611secured in a complementary threaded opening in the body of the extruderhead 30 and locked in position by a lock nut 36c. A positioning collar36d is formed coaxially about the torpedo 36 and engages the innercylindrical walls of the cavity 32 to form one wall of the cavity 32. Bymeans of rotating the torpedo 36 within the extruder head 30, thedistance between the frustro-conical tip 36a and the orifice 34 may bevaried, thereby to vary flow rates for material through the orifice 34.

The extrusion orifice 34 must be of a diameter and length to produce aproper pressure ratio with a wire of given diameter. It has been foundthat most satisfactory results are obtained where the ratio of thelength of the extrusion orifice divided by the sum of the diameter ofthe orifice minus the diameter of the wire, is approxi- L D-W where L isthe length of the orifice 34, D is the diameter of the orifice 34, and Wis the diameter of the Wire 22. Boththe pressure ratio requirements andthe requirement with regard to positioning the torpedo 36 with respectto the orifice 34 must be met in order to insure eflicient operations ofthe device.

In this illustrative embodiment, the sheathing 24 is cured by submersionin a receptacle 38 containing a bath B. The bath B may be of a materialsuch as glycerine which is elevated to a temperature of approximately350 F. Of course, a variation of other curing means may be employed.

From the foregoing, it will be appreciated that the extrusion apparatusdisclosed and described herein finds useful application for thefabrication of sheathing about a core.

Although the drawings and disclosures herein describe one particularembodiment of the present invention, other embodiments may beconstructed without departing from the teachings of the invention.Therefore, the following claims should be interpreted broadly consistentwith the spirit and scope of the invention.

What I claim is:

1. An extruder head for applying an extensible sheathing onto acompliant cable core in an apparatus which is free from any power sourcefor pulling a core through said extruder head comprising a body, saidbody having a central cavity formed therein and a circular extrusionorifice at one end in communication With said cavity, said cavity beingformed adjacent said orifice with frustroconical walls of decreasingdiameter toward said orifice, an extruder input pipe connected to saidbody in communication with said cavity at a location removed from saidorifice for the delivery of material to be extruded, a torpedopositioned within said head in alignment with said orifice, and meansadjustably mounting said torpedo within said cavity for movement towardand away from said orifice, said torpedo having a central cylindricalopening along its axis for the passage of a core into said extruderhead, through said torpedo and out of said extruder head through saidorifice, said torpedo being formed at its end adjacent said orifice withfrustro-conical walls of decreasing diameter toward said orifice, theincluded angle of said frustro-conical torpedo walls being less than theincluded angle of said frustro-conical cavity walls defining an annularoutlet passage of decreasing crosssection between said cavity Walls andsaid torpedo, said orifice being cylindrical in shape and having a ratioof its length divided by the same of its diameter minus the diameter ofthe central cylindrical opening of said torpedo, the flow of material tobe extruded through said outlet passage being the sole means oftransporting said core through said torpedo and said body.

2. An extruder head for applying an extensible sheathing onto acompliant cable core in an apparatus free from any power source forpulling a core through said extruder head for forming a sheathing abouta compliant wire of a given diameter comprising a body, said body havinga central cavity formed therein and a circular extrusion orifice at oneend in communication with said cavity, said cavity being formed adjacentsaid orifice with frustro-conical walls of decreasing diameter towardsaid orifice, delivery means in communication with said cavity at alocation removed from said orifice for the delivery of material to beextruded, said delivery means being angled to open into said cavity todeliver material into said cavity in thedirection of said orifice, and atorpedo positioned within said body and within said cavity in alignmentwith said orifice, said torpedo having a central opening along its axisfor the passage of said compliant wire into said extruder head, throughsaid torpedo and out of said extruder head through said orifice, saidtorpedo and the frustro-conical walls of said cavity defining an annularoutlet passage of decreasing cross-section toward said orifice betweensaid cavity wall and said torpedo, said orifice being cylindrical inshape and having a ratio of its length divided by the sum of itsdiameter minus the diameter of the central opening of said torpedo whichis approximately one, the flow of material to be extruded through saidoutlet being the sole means for transporting said compliant wire throughsaid tropedo and said body.

'3. An extruder head for forming a sheathing about a compliant wire of agiven diameter in an extrusion apparatus free from any power source forpulling said compliant wire through said head comprising a body, saidbody having a central cavity formed therein and a circular extrusionorifice at one end in communication with said cavity, said cavity beingformed adjacent said orifice with frustro-conical walls of decreasingdiameter toward said orifice, delivery means in communication with saidcavity at a location removed from said orifice for the delivery ofmaterial to be extruded, a torpedo positioned within said body andwithin said cavity inalignment with said orifice, said torpedo having acentral opening along its axis for the passage of said compliant wireinto said extruder head, through said tropedo and out of said extruderhead through said orifice, said torpedo and the frustro-conical walls ofsaid cavity defining an annular outlet passage directed toward saidorifice between said cavity wall and said torpedo, said orifice beingcylindrical in shape and having a ratio of its length divided by the sumof its diameter minus the diameter of the compliant wire which isapproximately one, the flow of material to be extruded through saidoutlet being the sole means for transporting said compliant wire throughsaid torpedo and said body, and means mounting said torpedo for axialmovement toward and away from said orifice for varying the volume ofsaid annular outlet passage to said orifice.

References Cited by the Examiner UNITED STATES PATENTS 325,363 9/1885Royle et a1. 1813 441,808 12/1890 Royle et a1 18-13 1,419,090 6/ 1922Williams 18-13 2,471,752 5/ 1949 Ingemanson. 2,522,364 9/1950 Grana 18132,979,431 4/ 1961 Perrault 18-13.

FOREIGN PATENTS 513,812 11/1920 France.

970,430 6/ 1950 France.

881,538 7/1953 Germany.

535,311 4/1941 Great Britain.

690,967 4/ 1953 Great Britain.

WILLIAM J. STEPHENSON, Primary Examiner.

ROBERT F. WHITE, MICHAEL V. BRINDISI,

Examiners. L. S. SQUIRES, Assistant Examiner.

1. AN EXTRUDER HEAD FOR APPLYING AN EXTENSIBLE SHEATHING ONTO ACOMPLIANT CABLE CORE IN AN APPARATUS WHICH IS FREE ANY POWER SOURCE FORPULLING A CORE THROUGH SAID EXTRUDER HEAD COMPRISING A BODY, SAID BODYHAVING A CENTRAL CAVITY FORMED THEREIN AND A CIRCULAR EXTRUSION ORIFICEAT ONE END IN COMMUNICATION WITH SAID CAVITY, SAID CAVITY BEING FORMEDADJACENT SAID ORIFICE WITH FRUSTROCONICAL WALLS OF DECREASING DIAMETERTOWARD SAID ORIFICE, AN EXTRUDER INPUT PIPE CONNECTED TO SAID BODY INCOMMUNICATION WITH SAID CAVITY AT A LOCATION REMOVED FROM SAID ORIFICEFOR THE DELIVERYL OF MATERIAL TO BE EXTRUDED A TORPEDO POSITIONED WITHINSAID HEAD IN ALIGNMENT WITH SAID ORIFICE, AND MEANS ADJUSTABLY MOUNTINGSAID TORPEDO WITHIN SAID CAVITY FOR MOVEMENT TOWARD AND AWAY FROM SAIDORIFICE, SAID TORPEDO HAVING A CENTRAL CYLINDRICAL OPENING ALONG ITSAXIS FOR THE PASSAGE OF A CORE INTO SAID EXTRUDER HEAD, THROUGH SAIDTORPEDO AND OUT OF SIAD EXTRUDER HEAD THROUGH SAID ORIFICE, SAID TORPEDOBEING FORMED AT ITS END ADJACENT SAID ORIFICE WITH FRUSTRO-CONICAL WALLSOF DECREASING DIAMETER TOWARD SAID ORIFICE, THE INCLUDED ANGLE OF SAIDFRUSTO-CONICAL TORPEDO WALLS BEING LESS THAN THE INCLUDED ANGLE OF SAIDFRUSTO-CONICAL CAVITY WALLS OF FINING AN ANNULAR OUTLET PASSAGE OFDECREASING CROSSSECTIOND BETWEEN SAID CAVITY WALLS AND SAID TORPEDO,SAID ORIFICE BEING CYLINDRICAL IN SHAPE AND HAVING A RATIO OF ITS LENGHTDIVIDED BY THE SAME OF ITS DIAMETER MINUS THE DIAMETER OF THE CENTRALCYLINDRICAL OPENING OF SAID TORPEDO, THE FLOW OF MATERIAL TO BE EXTRUDEDTHROUGH SAID OUTLET PASSAGE BEING THE SOLE MEANS OF TRANSPORTING SAIDCORE THROUGH SAID TORPEDO AND SAID BODY.